In conventional vehicle frame assemblies, bumper beams are fixedly mounted to frame rails at the front and rear ends of the vehicle. During a front or rear end collision in the longitudinal direction of the vehicle, the collision forces are received by the bumper beam and transmitted to the frame assembly via the connection between the bumper beam and the frame rails. In situations involving relatively high collision forces, transferring the collision energy directly to the vehicle frame assembly without some type of cushioning or dissipation can deform the frame rails or otherwise damage the frame assembly. Repairing damaged vehicle frame assemblies after a collision can be quite expensive.
To solve this problem, it has been known to intentionally weaken end portions of the frame rails so that the weakened end portions collapse during collision and dissipate some or all of the collision energy, thereby reducing the amount of collision energy transmitted to the remainder of the frame and the passenger compartment. These weakened end portions are referred to as “crush zones.” Providing these crush zones in the vehicle frame assembly adds significant complexity and increases the overall cost of manufacturing the vehicle frame assembly. Another problem with these crush zones is that they often tend to buckle and fold outwardly rather than collapsing only in the direction of the impact force (i.e. the longitudinal direction of the vehicle). This requires that there be sufficient room to accommodate such outward folding and ensure the proper energy dissipation.
As an alternative, it has been known to provide tubular crush zones that collapse in an accordion-like manner. An example of such an arrangement is disclosed in PCT Application WO 98/39106. The problem with this type of arrangement is that it is difficult to achieve satisfactory energy dissipation using only a pair of these accordion-type crush zones. Specifically, the amount of deformation allowed in these accordion-type crush zones is limited by its width. That is, once the accordion folds contact the opposing wall, there will be no further deformation of the crush zone and the remaining collision forces will be transmitted to the frame assembly undissipated.
Consequently, it would be desirable to provide a more effective alternative for providing crush zones to dissipate the collision energy during a front or rear end collision and thereby reduce the amount of energy being transferred to the vehicle frame assembly.
Further, in a frontal offset collision, impact occurs at one end of the bumper beam. During impact, the opposite end of the bumper beam pivots and tends to pivot the vehicle due to the rigid connection with the vehicle frame assembly. Specifically, as the end of the bumper beam which has been impacted is forced in towards the frame assembly, the opposite end swings in a direction away from the frame assembly. This tends to pull on that side of the frame assembly and pivot the vehicle in a yaw-type movement. Consequently, it would be desirable to prevent this pivoting movement of the vehicle during a frontal offset collision.